(1) Field of the Invention
The present invention relates to an electromagnetic type fuel injection valve, such as a fuel injection valve for injecting fuel into an induction system of an engine in an electronically controlled fuel injection system for an internal combustion engine, more particularly, to a construction of an injection hole.
(2) Related Art of the Invention
As a fuel injection valve to be used in an electronically controlled fuel injection system for an internal combustion engine, there is known a fuel injection valve having a valve body lifted by an electromagnet and a flat injection hole plate formed with a plurality of injection holes and provided downstream of a valve seat, for seating the valve body. Each of the injection holes is arranged concentrically in the injection hole plate and is inclined with respect to the axis of the valve body such that the distance from the axis is increased in the downstream direction.
In the open position, the fuel flowing through the lifted valve body and the valve seat is discharged with a wide angle with respect to the axis through the respective injection holes of the injection hole plate, to be thus dispersed (see Japanese Unexamined Patent Publication Kokai) 1-249960).
In such a type of fuel injection valve, the static flow rate adjustment of the fuel injection valve is performed by machining and honing the injection holes.
Furthermore, such a type of the fuel injection valve is positioned in the air intake passage downstream of a throttle valve, and a vacuum characteristics inspection when checking injection characteristics is performed by performing an injection through the fuel injection valve into a vacuum box maintained at a vacuum of -500 mm Hg by, for example, a vacuum pump.
Nevertheless, if the conditions associated with the honing process are not determined in consideration of the influence of the configuration of the inlet of the injection hole for the vacuum characteristics, a substantial flow resistance is induced at the inlet edge of the injection hole and causes a vaporization of the fuel due to a vacuum evaporation at the edge portion. This increases the possibility that the fuel injection valve does not meet standard, and a lowering of production yield.